Have you ever heard a variation of this?
Every immigration lawyer has heard it multiple times. Here are some explanations.
They are illegal, so they are criminals
Being in the US illegally is not necessarily a crime. Entering without inspection by an immigration officer, and re-entering after being removed, are crimes punishable with up to 6 months (first offence) or 2 years (2nd offence) in prison and minor fines.
About 40% of undocumented immigrants came to the US legally, but stayed longer than legally permitted. This overstay is a civil violation, not a criminal one. If you have ever driven over the speed limit, got a parking ticket, been creative on your tax return, etc, you have committed more crimes than someone who just overstayed a visa.
Why can't they get in line, like everyone else?
(Spoiler: there is no line for them)
It is much more difficult to immigrate to the US than most people realize. Many people believe that immigrants could immigrate legally if they wanted to. In fact, the opposite is true and immigrants are usually undocumented because they have no way to get legal status in the US.
Legal immigration almost always requires an employer or a family member to "sponsor" the immigrant. Most people come on nonimmigrant (temporary) visas initially, and later move to permanent residence (green cards). With very limited exceptions, a person cannot come to the US to work without prior immigration approval, and this approval must be based on an employer’s sponsorship.
Even if the worker has an employer to sponsor them, they must fit into strictly-defined categories of workers. These visa categories are very biased in favor of professional-level employees, or those with exceptional ability (athletes, scientists, performers, etc). There is no immigration category for the typical foreign worker with no third-level education or exceptional skills.
There are limited visas available for seasonal workers, but these still require a petitioning employer and are limited in numbers and time. In addition, the processing time can be 6 months or more. Employers often cannot predict the number of seasonal workers they will need that far in advance.
If you have a family member to sponsor your move to the US, you may be in luck….. or maybe not so much. If you are the spouse, parent or child of a US citizen (“immediate relative”), you may be able to move to the US in less than a year. Yes, even if you are married to a US citizen, you cannot live with your spouse until you have gone through the multi-step immigration process (unless you have an independent reason to legally live in the US, e.g. your own work visa).
If you are not an “immediate relative”, the green card process takes 3 to 22+ years, depending your relationship and your nationality. If you are the Chinese spouse of a permanent resident, your wait time is about 3 years now. If you are the Filipino brother of a US citizen, the wait is 22+ years. If you are the Venezuelan grandson of a US citizen, it doesn’t matter how difficult your life in Venezuela is right now, Grandma cannot sponsor you to come to the US.
Why can't they come legally, like my ancestors did?
(Spoiler: because it was much easier back then)*
Immigration has changed dramatically since many of your ancestors came here. In fact, there is a good chance that most people who immigrated over 75 years ago would not be admitted today.
If your ancestors came before 1882, there were no immigration laws to break so everyone came here legally. If they came before 1924, there were so few immigration laws that it was still difficult to come here illegally.
In the 1880s, legislation was passed aimed at limiting immigration – but unless you were Chinese, intellectually disabled or likely to become a public charge, you were sill welcome.
It wasn’t until 1892 that the US government started inspecting people who arrived in the US. The first, and best-known, of these inspection stations was Ellis Island. It was still very easy to pass the inspection. About 10,000 people passed through Ellis Island every day at its peak, and 99% of those were permitted to stay. Between 1900 and 1920, the US admitted over 14.5 million immigrants.
Immigration restrictions really started with legislation in 1921 and 1924, and has become increasingly more complex since then. Even in the late 1950s, it was much easier than today, however. My 82-year old father came from Ireland to Chicago to work (temporarily) in 1958. He got the equivalent of a green card just by applying directly at the US consulate, passing a cursory medical exam, convincing them that he wouldn’t become a communist and proving that he could support himself (he had funds for a week!).
* And are you sure your ancestors came legally??
Many immigrants who came here illegally over the years have benefitted from the various amnesty-type relief measures available. Maybe Granddad didn’t come legally after all, but was granted an amnesty…..
Don’t they have anchor babies so they can stay here?
No – unless this is a VERY long-term plan.
Anyone born in the US is automatically a US citizen. However, having a US citizen child does not automatically grant any right to the child’s parents to live in the US.
A US citizen child can petition for (“sponsor”) her parents to become permanent residents..... but only after the child turns 21. Up to then, an undocumented parent has no legal right to remain in the US simply because they have a US citizen child.
You can see that most people don't stay in the US illegally because it's just too much trouble or takes too much time to get the correct paperwork. They will never qualify, no matter how long they wait.
For more information on this topic, see these articles from the American Immigration Council:
 To get an idea of how difficult it is for a foreign national to move to the US to work, see the wizard here: http://www.martinvisalawyer.com/uploads/3/8/6/0/38600843/visa_wizard.pdf.
Elaine Martin has been practising US and global immigration law since 1997. She is an immigrant herself (from Ireland), so has a special understanding of the legal and emotional challenges involved in relocating to a new country.